1. Field of the Invention
The present invention relates to new polymers and use of such polymers as a resin binder component for photoresist compositions, particularly chemically-amplified positive-acting resists.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble.
In general, photoresist compositions comprise at least a resin binder component and a photoactive agent. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4, both incorporated herein by reference for their teaching of photoresist compositions and methods of making and using the same.
More recently, "chemically-amplified" resists have become of increased interest, especially for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically resists, certain cationic photoinitiators have been used to induce cleavage of certain "blocking" groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a base soluble functional group is provided, e.g., carboxylic acid or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer.
Also recently interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation having wavelengths of about 250 nm or less, or even about 200 nm or less, such as wavelengths of about 248 nm and 193 nm. Such photoresists offer the potential of forming images of smaller features than may be possible at longer wavelength exposures.
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-micron and sub-half micron features.
For example, many current chemically-amplified positive resists require use of relatively strong photogenerated acids and/or use of a relatively high temperature post-exposure bake (PEB) treatment to conduct the desired deprotection reaction.
However, in many instances, use of photoacid generators that produce weaker photoacids and use of relatively low PEB temperatures (e.g. 110.degree. C. or less) would be a significant advantage. For example, if the desired deprotection chemistry could be carried out with a weaker acid, a wider range of photoacid generators could be potentially employed. Moreover, the industry continually seeks use of lowered post-exposure-bake temperatures because of uniformity considerations.
It thus would be desirable to have new photoresist compositions, particularly positive resist compositions that can be effectively imaged at short wavelengths, particularly sub-200 nm wavelengths such as 193 nm. It would be particularly desirable to have new chemically amplified positive photoresist compositions that employ photoacid generators that produce weaker photoacids and that can be activated with relatively low PEB temperatures.